1. Field of the Invention
This invention relates generally to periscopes and, more particularly, to low-cost periscopes that are immersible in fluids such as water.
2. Description of the Prior Art
Periscopes are well-known optical instruments that deviate or displace an observer's line of sight to provide a perspective from a distant position that would otherwise be inaccessible or dangerous. This is accomplished by arranging reflecting elements, such as mirrors or prisms, in a tubular structural member such that incoming light rays from an object are collected at one end of the instrument, distant from the observer, and directed along a folded optical path to the proximal end located near the observer's direct line of sight.
The fundamental and simplest form of periscope consists of a pair of parallel reflecting surfaces arranged in oppositely facing directions along a longitudinally extending tube of rectangular or circular cross-section. The reflecting surfaces here are either prisms or plane mirrors. One of the reflecting surfaces is placed at the distal end of the tube to fold incoming rays by 90-degrees for travel along the length of its longitudinal axis. The other mirror is placed at the proximal end, some predetermined distance from the distal end, to intercept oncoming light and fold it through another 90-degrees for travel downstream to the observer.
In its most fundamental form, the periscope has been used for some time now to provide otherwise inaccessible views in a variety of environments ranging from its relatively safe use as a hydroscope for inspecting underwater objects such as boat hulls and pier structures to its more dangerous use as a visual aid in tanks or other military vehicles.
More complex forms are also known and are often used for military and navigational applications. Such systems typically employ complex optical elements beyond the just the two reflecting surfaces of the fundamental form. Usually, complex optics are placed in the intervening space between purely reflecting elements, or straddle one or more of them, to provide a variety of functions including magnification, measurement, distance ranging, targeting, or increased field of view. Typical examples here include the rather lengthy telescoping submarine periscope and the compact sextant periscope for celestial navigation during flight.
Aside from industrial, commercial, and military uses, periscopes have long been used in their fundamental form as toys and as learning aids for teaching optical principles. For this purpose, they need to be low-cost, robust, and simple to use and manufacture. One known approach to satisfying the foregoing requirements is shown and described in U.S. Pat. No. 4,887,893 entitled "PERISCOPE WITH ONE PIECE HOUSING AND MIRROR HOLDING ELEMENTS" issued on Dec. 19, 1989 in the name of Lennart Dehlgren. Dehlgren's primary concern is with low-cost and ease of assembly of a toy periscope. To accomplish these goals, a blow molded plastic tube is fitted with two snap-in end caps which carry the necessary reflecting mirrors for a periscope of simple form. However, there is no consideration given to the use of a periscope in a fluid environment such as water or one that has additional functionality as a learning tool or action toy.
Consequently, it is a primary object of the present invention to provide a low-cost periscope for use as a toy or learning tool.
It is another object of the present invention to provide a periscope that can be used to provide a view under the water.
It is yet another object of the present invention to provide a simple periscope that is capable of viewing along two different paths under water.
It is still another object of the present invention to provide a low-cost, simple to use periscope that is adapted for use either as a toy or a learning tool for use in a variety of aquatic environments where children play and learn.
Other objects of the invention will be apparent and will appear hereinafter in the following detailed description.